Laser welding head with dual movable mirrors providing beam movement and laser welding systems and methods using same

ABSTRACT

A laser welding head with movable mirrors may be used to perform welding operations, for example, with wobble patterns and/or seam finding/tracking and following. The movable mirrors provide a wobbling movement of one or more beams within a relatively small field of view, for example, defined by a scan angle of 1-2°. The movable mirrors may be galvanometer mirrors that are controllable by a control system including a galvo controller. The laser welding head may also include a diffractive optical element to shape the beam or beams being moved. The control system may also be used to control the fiber laser, for example, in response to the position of the beams relative to the workpiece and/or a sensed condition in the welding head such as a thermal condition proximate one of the mirrors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/187,235 filed Jun. 20, 2016, which claims the benefit of U.S.Provisional Patent Application Ser. No. 62/182,211 filed on Jun. 19,2015 and U.S. Provisional Patent Application Ser. No. 62/294,731 filedon Feb. 12, 2016, both of which are fully incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to laser welding and more particularly, toa laser welding head with dual movable mirrors providing beam movementand laser welding systems and methods using same.

BACKGROUND INFORMATION

Lasers such as fiber lasers are often used for materials processingapplications such as welding. A conventional laser welding head includesa collimator for collimating laser light and a focus lens for focusingthe laser light to a target area to be welded. The beam may be moved invarious patterns to facilitate welding two structures along a seam, forexample, using a stir welding technique. One way to move the beam forstir welding is to rotate the beam using rotating prism optics to form arotating or spiral pattern. Another way to move a beam for welding is topivot or move the entire weld head on an X-Y stage to form a zig zagpattern. These conventional methods of moving the beam to perform weldpatterns do not allow quick and precise movements of the beam.

SUMMARY

Consistent with an embodiment, a laser welding head includes acollimator configured to be coupled to an output fiber of a fiber laserand at least first and second movable mirrors configured to receive acollimated laser beam from the collimator and to move the beam in firstand second axes within only a limited field of view defined by a scanangle of about 1-2°. The laser welding head also includes a focus lensconfigured to focus the laser beam relative to a workpiece while thebeam is moved.

Consistent with another embodiment, a laser welding head includes acollimator configured to be coupled to an output fiber of a fiber laser,at least first and second movable mirrors configured to receive acollimated laser beam from the collimator and to move the beam in firstand second axes, and at least first and second thermal sensors proximatethe first and second movable mirrors, respectively, and configured todetect a thermal condition. The laser welding head also includes a focuslens configured to focus the laser beam.

Consistent with a further embodiment, a laser welding head includes acollimator module including a collimator configured to be coupled to anoutput fiber of a fiber laser and a wobbler module coupled to thecollimator module. The wobbler module includes at least first and secondmovable mirrors configured to receive a collimated laser beam from thecollimator and to move the beam in first and second axes. The laserwelding head also includes a core block module coupled to the wobblermodule. The core block module includes at least a focus lens configuredto focus the laser beam.

Consistent with yet another embodiment, a laser welding system includesa fiber laser including an output fiber and a welding head coupled tothe output fiber of the fiber laser. The welding head includes acollimator configured to be coupled to an output fiber of a fiber laser,at least first and second movable mirrors configured to receive acollimated laser beam from the collimator and to move the beam in firstand second axes, and a focus lens configured to focus the laser beam.The laser welding system also includes a control system for controllingat least the fiber laser and positions of the mirrors.

Consistent with yet another embodiment, a laser welding head includes acollimator configured to be coupled to an output fiber of a fiber laser,at least first and second movable mirrors configured to receive acollimated laser beam from the collimator and to move the beam in firstand second axes, and a focus lens configured to focus the laser beam.The laser welding head also includes at least one of a gas assistaccessory and an air knife accessory proximate the focus lens to assistwelding.

Consistent with yet another embodiment, a laser welding head includes acollimator configured to be coupled to an output fiber of a fiber laser,at least one diffractive optical element configured to receive acollimated laser beam from the collimator and to shape the collimatedlaser beam, and at least first and second movable mirrors configured toreceive a shaped laser beam from the diffractive optical element and tomove the shaped beam in first and second axes. The laser welding headalso includes a focus lens configured to focus the laser beam relativeto a workpiece while the beam is moved.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages will be better understood byreading the following detailed description, taken together with thedrawings wherein:

FIG. 1 is a schematic block diagram of a system including a laserwelding head with dual movable mirrors, consistent with an embodiment ofthe present disclosure.

FIG. 1A is a schematic diagram of a focused laser beam with a relativelysmall range of movement provided by dual mirrors for purposes of seamfinding and/or wobbling, consistent with an embodiment of the presentdisclosure.

FIGS. 2A-2D are schematic diagrams illustrating different wobblepatterns capable of being produced by a welding head including dualmirrors for beam movement, consistent with an embodiment of the presentdisclosure.

FIG. 3A is a micrograph of a welded workpiece with a weld bead formed bya laser using stir welding with a FIG. 8 wobble pattern, consistent withan embodiment of the present disclosure.

FIG. 3B is a micrograph of a cross-section of the welded workpiece andweld bead shown in FIG. 3A.

FIG. 3C is a micrograph of a welded workpiece with a weld bead formed bya laser without a wobble pattern.

FIG. 3D is a micrograph of a cross-section of the welded workpiece andweld bead shown in FIG. 3C.

FIG. 4 is an exploded view of a laser welding head with dual movablemirrors for beam movement, consistent with an embodiment of the presentdisclosure.

FIGS. 5 and 6 are perspective views of a collimator module used in thelaser welding head shown in FIG. 4.

FIG. 7 is a perspective view of a wobbler module used in the laserwelding head shown in FIG. 4.

FIG. 8 is an exploded view of the wobbler module used in the laserwelding head shown in FIG. 4.

FIG. 9 is a partially cross-sectional side view of the wobbler moduleused in the laser welding head shown in FIG. 4.

FIG. 10 is perspective view of the inside of the wobbler module with awater cooled limiting aperture and thermal sensors.

FIG. 11 is an exploded view of a core block module including a focus andwindow housing used in the laser welding head shown in FIG. 4.

FIG. 12 is an exploded view of the focus and window housing with aprotective window used in the laser welding head shown in FIG. 4.

FIGS. 13 and 14 are perspective views of the laser welding head shown inFIG. 4 with the collimator module, wobbler module, and core block moduleassembled together and emitting a focused beam.

FIG. 15 is a schematic diagram of the beam path within the laser weldinghead shown in FIGS. 13 and 14.

FIG. 16 is a schematic block diagram of a laser welding head with dualmovable mirrors and diffractive optics, consistent with an embodiment ofthe present disclosure.

FIGS. 17A and 17B illustrate a circular beam spot and a shapedrectangular beam spot produced by diffractive optics, respectively.

FIG. 17C illustrates a donut-shaped beam spot produced by beam shapingoptics.

FIGS. 18A-18C illustrate rectangular beam spots of different sizesproduced by different diffractive optics.

FIG. 19 illustrates a pattern of beam spots produced by a multi-beamfiber laser coupled to a laser welding head, consistent with embodimentsof the present disclosure.

FIG. 20 illustrates a pattern of shaped beam spots produced by amulti-beam fiber laser coupled to a laser welding head includingdiffractive optics, consistent with embodiments of the presentdisclosure.

DETAILED DESCRIPTION

A laser welding head with movable mirrors, consistent with embodimentsof the present disclosure, may be used to perform welding operations,for example, with wobble patterns and/or seam finding/tracking andfollowing. The movable mirrors provide a wobbling movement of one ormore beams within a relatively small field of view, for example, definedby a scan angle of 1-2°. The movable mirrors may be galvanometer mirrorsthat are controllable by a control system including a galvo controller.The laser welding head may also include a diffractive optical element toshape the beam or beams being moved. The control system may also be usedto control the fiber laser, for example, in response to the position ofthe beams relative to the workpiece and/or a sensed condition in thewelding head such as a thermal condition proximate one of the mirrors.

Referring to FIG. 1, a laser welding system 100 includes a laser weldinghead 110 coupled to an output fiber 111 of a fiber laser 112 (e.g., witha connector 111 a). The laser welding head 110 may be used to performwelding on a workpiece 102, for example, by welding a seam 104 to form aweld bead 106. The laser welding head 110 and/or the workpiece 102 maybe moved relative to each other along the direction of the seam 104. Thelaser welding head 110 may be located on a motion stage 114 for movingthe welding head 110 relative to the workpiece 102 along at least oneaxis, for example, along the length of the seam 104. Additionally oralternatively, the workpiece 102 may be located on a motion stage 108for moving the workpiece 102 relative to the laser welding head 110.

The fiber laser 112 may include an Ytterbium fiber laser capable ofgenerating a laser in the near infrared spectral range (e.g., 1060-1080nm). The Ytterbium fiber laser may be a single mode or multi-modecontinuous wave Ytterbum fiber laser capable of generating a laser beamwith power up to 1 kW in some embodiments and higher powers up to 50 kWin other embodiments. Examples of the fiber laser 112 include the YLR SMSeries or YLR HP Series lasers available from IPG Photonics Corporation.The fiber laser 112 may also include a multi-beam fiber laser, such asthe type disclosed in International Application No. PCT/US2015/45037filed 13 Aug. 2015 and entitled Multibeam Fiber Laser System, which iscapable of selectively delivering one or more laser beams throughmultiple fibers.

The laser welding head 110 generally includes a collimator 122 forcollimating the laser beam from the output fiber 111, at least first andsecond movable mirrors 132, 134 for reflecting and moving the collimatedbeam 116, and a focus lens 142 for focusing and delivering a focusedbeam 118 to the workpiece 102. In the illustrated embodiment, a fixedmirror 144 is also used to direct the collimated laser beam 116 from thesecond movable mirror 134 to the focus lens 142. The collimator 122, themovable mirrors 132, 134, and the focus lens 142 and fixed mirror 144may be provided in separate modules 120, 130, 140 that may be coupledtogether, as will be described in greater detail below. The laserwelding head 110 may also be constructed without the fixed mirror 144,for example, if the mirrors 132, 134 are arranged such that the light isreflected from the second mirror 134 toward the focus lens 142.

The movable mirrors 132, 134 are pivotable about different axes 131, 133to cause the collimated beam 116 to move and thus to cause the focusedbeam 118 to move relative to the workpiece 102 in at least two differentperpendicular axes 2, 4. The movable mirrors 132, 134 may begalvanometer mirrors that are movable by galvo motors, which are capableof reversing direction quickly. In other embodiments, other mechanismsmay be used to move the mirrors such as stepper motors. Using themovable mirrors 132, 134 in the laser welding head 110 allows the laserbeam 118 to be moved precisely, controllably and quickly for purposes ofseam finding and following and/or beam wobbling without having to movethe entire welding head 110 and without using rotating prisms.

In an embodiment of the welding head 110, movable mirrors 132, 134 movethe beam 118 within only a relatively small field of view (e.g., lessthan 30×30 mm) by pivoting the beam 118 within a scan angle α of lessthan 10° and more particularly about 1-2°, as shown in FIG. 1A, therebyallowing the beam to wobble. In contrast, conventional laser scan headsgenerally provide movement of the laser beam within a much larger fieldof view (e.g., larger than 50×50 mm and as large as 250×250 mm) and aredesigned to accommodate the larger field of view and scan angle. Thus,the use of the movable mirrors 132, 134 to provide only a relativelysmall field of view in the laser welding head 110 is counter-intuitiveand contrary to the conventional wisdom of providing a wider field ofview when using galvo scanners. Limiting the field of view and the scanangle provides advantages when using galvo mirrors in the welding head110, for example, by enabling faster speeds, allowing use with lessexpensive components such as lenses, and by allowing use withaccessories such as air knife and/or gas assist accessories.

Because of the smaller field of view and scan angle in the exampleembodiment of the welding head 110, the second mirror 134 may besubstantially the same size as the first mirror 132. In contrast,conventional galvo scanners generally use a larger second mirror toprovide for the larger field of view and scan angle and the largersecond mirror may limit the speed of movement in at least one axis. Asmaller sized second mirror 134 (e.g., about the same size as the firstmirror 132) in the welding head 110 thus enables the mirror 134 to movewith faster speeds as compared to larger mirrors in conventional galvoscanners providing large scan angles.

The focus lens 142 may include focus lenses known for use in laserwelding heads and having a variety of focal lengths ranging, forexample, from 100 mm to 1000 mm. Conventional laser scan heads usemulti-element scanning lenses, such as an F theta lens, a fieldflattening lens, or a telecentric lens, with much larger diameters(e.g., a 300 mm diameter lens for a 33 mm diameter beam) to focus thebeam within the larger field of view. Because the movable mirrors 132,134 are moving the beam within a relatively small field of view, alarger multi-element scanning lens (e.g., an F theta lens) is notrequired and not used. In one example embodiment of the welding head 110consistent with the present disclosure, a 50 mm diameter plano convexF300 focus lens may be used to focus a beam having a diameter of about40 mm for movement within a field of view of about 15×5 mm. The use ofthe smaller focus lens 142 also allows additional accessories, such asair knife and/or gas assist accessories, to be used at the end of thewelding head 110. The larger scanning lenses required for conventionallaser scan heads limited the use of such accessories.

Other optical components may also be used in the laser welding head 110such as a beam splitter for splitting the laser beam to provide at leasttwo beam spots for welding (e.g., on either side of the weld).Additional optical components may also include diffractive optics andmay be positioned between the collimator 122 and the mirrors 132, 134,as will be described in greater detail below.

A protective window 146 may be provided in front of the lens 142 toprotect the lens and other optics from the debris produced by thewelding process. The laser welding head 110 may also include a weldinghead accessory 116, such as an air knife for providing high velocity airflow across the protective window 146 or focus lens 142 to remove thedebris and/or a gas assist accessory to deliver shield gas coaxially oroff-axis to the weld site to suppress weld plume. Thus, the laserwelding head 110 with movable mirrors is capable of being used withexisting welding head accessories.

The illustrated embodiment of the laser welding system 100 also includesa detector 150, such as a camera, for detecting and locating the seam104, for example, at a location in advance of the beam 118. Although thecamera/detector 150 is shown schematically at one side of the weldinghead 110, the camera/detector 150 may be directed through the weldinghead 110 to detect and locate the seam 104.

The illustrated embodiment of the laser welding system 100 furtherincludes a control system 160 for controlling the fiber laser 112, thepositioning of the movable mirrors 132, 134, and/or the motion stages108, 114, for example, in response to sensed conditions in the weldinghead 110, a detected location of the seam 104, and/or movement and/or aposition of the laser beam 118. The laser welding head 110 may includesensors such as first and second thermal sensors 162, 164 proximate therespective first and second movable mirrors 132, 134 to sense thermalconditions. The control system 160 is electrically connected to thesensors 162, 164 for receiving data to monitor the thermal conditionsproximate the movable mirrors 132, 134. The control system 160 may alsomonitor the welding operation by receiving data from the camera/detector150, for example, representing a detected location of the seam 104.

The control system 160 may control the fiber laser 112, for example, byshutting off the laser, changing the laser parameters (e.g., laserpower), or adjusting any other adjustable laser parameter. The controlsystem 160 may cause the fiber laser 112 to shut off in response to asensed condition in the laser welding head 110. The sensed condition maybe a thermal condition sensed by one or both of the sensors 162, 164 andindicative of a mirror malfunction resulting in high temperatures orother conditions caused by the high power laser.

The control system 160 may cause the fiber laser 112 to shut off bytriggering a safety interlock. A safety interlock is configured betweenthe output fiber 111 and the collimator 122 such that the safetyinterlock condition is triggered and the laser is shut off when theoutput fiber 111 is disconnected from the collimator 122. In theillustrated embodiment, the laser welding head 110 includes an interlockpath 166 that extends the safety interlock feature to the movablemirrors 132, 134. The interlock path 166 extends between the outputfiber 111 and the control system 160 to allow the control system 160 totrigger the safety interlock condition in response to potentiallyhazardous conditions detected in the laser welding head 110. In thisembodiment, the control system 160 may cause the safety interlockcondition to be triggered via the interlock path 166 in response to apredefined thermal condition detected by one or both sensors 162, 164.

The control system 160 may also control the laser parameters (e.g.,laser power) in response to movement or a position of the beam 118without turning off the laser 112. If one of the movable mirrors 132,134 moves the beam 118 out of range or too slowly, the control system160 may reduce the laser power to control the energy of the beam spotdynamically to avoid damage by the laser. The control system 160 mayfurther control selection of laser beams in a multi-beam fiber laser.

The control system 160 may also control the positioning of the movablemirrors 132, 134 in response to the detected location of the seam 104from the camera/detector 150, for example, to correct the position ofthe focused beam 118 to find, track and/or follow the seam 104. Thecontrol system 160 may find the seam 104 by identifying a location ofthe seam 104 using the data from the camera/detector 150 and then movingone or both of the mirrors 132, 134 until the beam 118 coincides withthe seam 104. The control system 160 may follow the seam 104 by movingone or both of the mirrors 132, 134 to adjust or correct the position ofthe beam 118 continuously such that the beam coincides with the seam 104as the beam 118 moves along the seam to perform the weld. The controlsystem 160 may also control one or both of the movable mirrors 132, 134to provide the wobble movement during welding, as described in greaterdetail below.

The control system 160 thus includes both laser control and mirrorcontrol working together to control both the laser and the mirrorstogether. The control system 160 may include, for example, hardware(e.g., a general purpose computer) and software known for use incontrolling fiber lasers and galvo mirrors. Existing galvo controlsoftware may be used, for example, and modified to allow the galvomirrors to be controlled as described herein.

FIGS. 2A-2D illustrate examples of wobble patterns that may be used toperform stir welding of a seam 204. As used herein, “wobble” refers toreciprocating movement of a laser beam (e.g., in two axes) and within arelatively small field of view defined by a scan angle of less than 10°.FIGS. 2A and 2B show a circular pattern and a FIG. 8 pattern,respectively, being formed sequentially along the seam 204. FIGS. 2C and2D show a zig-zag pattern and an undulating pattern, respectively, beingformed along the seam 204. Although certain wobble patterns areillustrated, other wobble patterns are within the scope of the presentdisclosure. One advantage of using the movable mirrors in the laserwelding head 110 is the ability to move the beam according to a varietyof different wobble patterns.

FIGS. 3A-3D illustrate a comparison of welds formed on 6061 T6 Al by aFIG. 8 wobble pattern (FIGS. 3A and 3B) compared to a conventionalnon-manipulated beam (FIGS. 3C and 3D). In one example (FIGS. 3A and3B), a two pieces of aluminum 6061-T6 alloy are welded with a 2 mmdiameter beam spot moving with a FIG. 8 pattern at 90° with a 300 Hzwobble, a power of 2.75 kW, a speed of 3.5 m/min and with a 0.012 in.gap. In the other example (FIGS. 3C and 3D), two pieces of aluminum6061-T6 alloy are welded with a beam spot with no wobble, a power of 2.0kW, a speed of 3.5 m/min and with a 0.012 in. gap. As shown, the weldquality on the surface with the FIG. 8 wobble is improved as compared tothe non-manipulated beam. In particular, uniformity through the weld isimproved as shown in FIG. 3A compared to FIG. 3C. The cross section inFIG. 3B also shows less reduction in area at the weld (as compared toFIG. 3D), which is due to the FIG. 8 wobble pattern bridging the gap ofthe seam 204 more effectively. The laser welding systems and methodsdescribed herein may also be used to improve welding with materials,such as titanium, that are typically difficult to weld.

FIGS. 4-15 illustrate an embodiment of the laser welding head 410 ingreater detail. Although one specific embodiment is shown, otherembodiments of the laser welding head and systems and methods describedherein are within the scope of the present disclosure. As shown in FIG.4, the laser welding head 410 includes a collimator module 420, awobbler module 430, and a core block module 440. The wobbler module 430includes the first and second movable mirrors as discussed above and iscoupled between the collimator module 420 and the core block module 440.

FIGS. 5 and 6 show the collimator module 420 in greater detail. As shownin FIG. 5, an input end 421 of the collimator module 420 is configuredto be coupled to an output fiber connector and includes a fiberinterlock connector 425 that connects to the output fiber connector (notshown) to provide a safety interlock for when the output fiber isdisconnected. As shown in FIG. 6, an output end 423 of the collimatormodule 420 is configured to be coupled to the wobbler module 430 (seeFIG. 4) and includes a fiber interlock connector 427 to extend thesafety interlock path into the wobbler module 430. The collimator module420 may include a collimator (not shown) with a fixed pair of collimatorlenses such as the type known for use in laser welding heads. In otherembodiments, the collimator may include other lens configurations, suchas movable lenses, capable of adjusting the beam spot size and/or focalpoint.

FIGS. 7-10 show the wobbler module 430 in greater detail. Theillustrated embodiment of the wobbler module 430 includes an inputaperture 431 for coupling to the collimator module 420 and an outputaperture 433 for coupling to the core block module 440 (see FIG. 4). Theinput aperture 431 may include a water cooled limiting aperture.

As shown in FIG. 8, the illustrated embodiment of the wobbler module 430also includes first and second galvanometers 436, 438 for moving galvomirrors 432, 434 about different perpendicular axes. Galvanometers knownfor use in laser scanning heads may be used. The galvanometers 436, 438may include connections 437 for connecting to a galvo controller (notshown). The galvo controller may include hardware and/or software forcontrolling the galvanometers to control movement of the mirrors andthus movement and/or positioning of the laser beam. Known galvo controlsoftware may be used and may be modified to provide the functionalitydescribed herein, for example, the seam finding, the wobbler patterns,and communication with the laser.

As shown in FIG. 7, the wobbler module 430 includes a fiber interlockconnector 435 for connecting to the collimator fiber interlock connector427. The wobbler module 430 also includes a galvo fiber interlockconnector 437 for connecting to the galvo controller. The safetyinterlock is thus extended to the wobbler module 430 and to the galvocontroller. The galvo controller may be configured to trigger a safetyinterlock condition, for example, in response to sensed conditionswithin the wobbler module 430.

As shown in FIGS. 9 and 10, the wobbler module 430 includes thermalprobes 462, 464 proximate each of the respective mirrors 432, 434. Thethermal probes 462, 464 sense a thermal condition (e.g., temperature) atthe respective locations within the wobbler module 430 and may beconnected via the galvo connections 437 to the galvo controller. Thegalvo controller may thus monitor the thermal probes 462, 464 todetermine if a predefined condition occurs, such as a high temperatureindicating a potentially hazardous condition within the wobbler module430. If one of the movable mirrors 432, 434 malfunctions, for example,the high power laser directed into the wobbler module 430 may not bereflected properly and may cause the hazardous condition. The galvocontroller may thus trigger the safety interlock to shut down the laserin response to the hazardous condition. The thermal probes may includeknown sensors such as bimetal strips inside of ceramic.

FIG. 11 shows the core block module 440 in greater detail. The coreblock module 440 includes a fixed mirror (not shown) that redirects thebeam received from the wobbler module 430 to a focus lens 442 and thento the workpiece. As shown, the core block module 440 includes a coreblock housing 441 and a focus and window housing 443 coupled to one sideof the core block housing 441. A camera module (not shown) may becoupled to an opposite side of the core block housing 441 for monitoringthe focused beam and/or the workpiece within the field of view providedthrough the focus and window housing 443.

The focus and window housing 443 contains the focus lens 442 and aprotective window 446. As shown in FIG. 12, the protective window 446may be removable and replaceable. The focus and window housing 443 alsocontains a window status monitoring circuit 470 with sensors such as athermistor 472 and photodiode 474 to monitor a status of the protectivewindow 446. The core block housing 441 further includes a statusmonitoring connector 475 for connecting to the status monitoring circuit470 in the focus and window housing 443 and a welding monitor connector477 for connecting to a welding head monitor (not shown).

FIGS. 13 and 14 show the assembled laser welding head 410 with each ofthe modules 420, 430, 440 coupled together and emitting a focused beam418. A laser beam coupled into the collimator module 420 is collimatedand the collimated beam is directed to the wobbler module 430. Thewobbler module 430 moves the collimated beam using the mirrors anddirects the moving collimated beam to the core block module 440. Thecore block module 440 then focuses the moving beam and the focused beam418 is directed to a workpiece (not shown).

FIG. 15 shows the path of a collimated beam 416 inside of the wobblermodule 430 and the core block module 440 when coupled together. Asshown, the collimated beam 416 input to the wobbler module is reflectedfrom the first galvo mirror 432 to the second galvo mirror 434 and thenreflected from the fixed mirror 444 inside the core block module andoutput from the core block module. The fixed mirror 444 may be aninfrared mirror to allow use with a camera for monitoring the beam 416.

Referring to FIG. 16, further embodiments of a laser welding head 1610with movable mirrors and a laser welding system are described in greaterdetail. This embodiment of the laser welding head 1610 further includesat least one beam shaping diffractive optical element 1626 for shapingthe beam. The beam shaping diffractive optical element 1626 is locatedbetween a collimator 1622 and movable mirrors 1632, 1634 in the weldinghead 1610. The beam shaping diffractive optical element 1626 shapes thecollimated beam and the shaped beam is then moved by the mirrors 1632,1634, for example, as described above.

One example of the beam shaping diffractive optical element 1682includes a top hat beam shaping element that receives an input beam witha Gaussian profile and circular beam spot, as shown in FIG. 17A, andproduces a shaped beam with a uniform square or “top hat” profile and arectangular or square beam spot, as shown in FIG. 17B. Other beamshaping diffractive optical elements may include, without limitation, adiffractive beam splitting element that converts an input beam into a 1or 2 dimensional array of beamlets, a ring generator element that shapesan input beam into a ring or a series of rings, and a diffractive vortexlens that shapes an input beam into a donut-shaped ring, as shown inFIG. 17C.

Different beam shaping diffractive optical elements 1626 may thus beused providing different shapes and/or sizes of beams. A donut shapedbeam spot may also have a more uniform power distribution by eliminatinga high power concentration at the center of the beam. As shown in FIGS.18A-18C, different diffractive optical elements may provide rectangularbeams having different sizes, thereby enabling different “brush sizes”and resolutions for welding and other applications. Smaller beam spotsor “brush sizes” may be used, for example, for smaller areas or aroundedges where a higher resolution is desired.

In an embodiment, the beam shaping diffractive optical element 1626 islocated in a beam shaping module 1624, which may be removably positionedbetween a collimator module 1620 and a wobbler module 1630, for example,as described above. Thus, beam shaping modules 1624 with differentdiffractive optics may be used interchangeably in the welding head 1610.The beam shaping module 1624 may also provide a safety interlock path1666 as described above.

In yet another embodiment, the welding head 1610 may be coupled to amulti-beam fiber laser 1612 capable of selectively delivering multiplebeams. One example of a multi-beam fiber laser is described in greaterdetail in International Application No. PCT/US2015/45037 filed 13 Aug.2015 and entitled Multibeam Fiber Laser System, which is fullyincorporated herein by reference. In one embodiment, a Ytterbum fiberlaser provides an output of 1070 nm but any variety of wavelengths iscontemplated, such that Er, Th, Ho, doped fibers, or some combinationthereof, are contemplated not to mention fiber lasers in which theoutput is frequency shifted by virtue of non-linear optical crystals,Raman fibers and the like. The multiple beams may have differentcharacteristics such as different modes, powers, energy densities,profiles and/or sizes. FIG. 19, for example, shows multiple beams havingdifferent sizes. Multiple beams may be delivered at the same time orindividual beams with different characteristics may be deliveredseparately and selectively at different times to provide differentoperations (e.g., heating, welding, and post-processing). Multiple beamsmay also be shaped by the diffractive optics 1626 to produce multipleshaped beams, for example, as shown in FIG. 20. The shape and/or size ofmultiple beams may thus be changed for different operations orapplications using the multi-beam fiber laser 1612 and/or differentdiffractive optical elements 1626. For some welding applications, forexample, one or more beams may be shaped in a ring or donut shape toprovide more uniform power distribution.

Accordingly, a laser welding head with movable mirrors, consistent withembodiments described herein, allows improved control over the movement,size, and/or shape of a laser beam used for various weldingapplications. Embodiments of the laser welding head with movable mirrorsand the welding systems and methods described herein may thus be used toform stronger, smoother and more uniform welds.

While the principles of the invention have been described herein, it isto be understood by those skilled in the art that this description ismade only by way of example and not as a limitation as to the scope ofthe invention. Other embodiments are contemplated within the scope ofthe present invention in addition to the exemplary embodiments shown anddescribed herein. Modifications and substitutions by one of ordinaryskill in the art are considered to be within the scope of the presentinvention, which is not to be limited except by the following claims.

What is claimed is:
 1. A laser welding method comprising: generating araw laser beam from a laser; collimating the raw laser beam in a weldinghead; reflecting the collimated laser beam from at least one movablemirror in the welding head and moving the at least one movable mirror tomove the beam relative to a workpiece, wherein the movement is onlywithin a limited field of view defined by a scan angle of about 1-2°;and focusing the moving beam on the workpiece to perform welding.
 2. Thelaser welding method of claim 1 further comprising moving at least oneof the laser welding head and the workpiece relative to each other whilemoving the beam with the movable mirror.
 3. The laser welding method ofclaim 1 wherein the at least one movable mirror includes at lease twomovable mirrors for moving the beam in at least two different axes. 4.The laser welding method of claim 1 further comprising controllingmovement of the at least one movable mirror such that the beam moveswith a wobble pattern on the workpiece during welding.
 5. The laserwelding method of claim 1 wherein at least a portion of the workpiecebeing welded is Aluminum.
 6. The laser welding method of claim 1 whereingenerating the laser beam includes generating a laser beam in a nearinfrared spectral range from an Ytterbium fiber laser.
 7. The laserwelding method of claim 1 wherein generating the laser beam includesgenerating a laser beam from a fiber laser with an active fiber selectedfrom the group consisting of Er, Th, Ho, doped fibers, and combinationsthereof.
 8. The laser welding method of claim 1 further comprisingcontrolling movement of the at least one moveable mirror such that thebeam follows a seam to be welded.
 9. The laser welding method of claim 9further comprising detecting a location of the seam to be welded inadvance of the seam, and wherein movement is controlled to adjust aposition of the beam in response to the detected location of the seam tobe welded.
 10. The laser welding method of claim 9 further comprisingcontrolling movement of at least one movable mirror such that the beammoves with a wobble pattern over the seam to be welded.
 11. The laserwelding method of claim 1 further comprising shaping the collimatedbeam.
 12. The laser welding method of claim 11 wherein shaping the laserbeam includes passing the collimated laser beam through diffractiveoptics.
 13. The laser welding method of claim 1 further comprisingadjusting laser power in response to movement and/or a position of thebeam.
 14. The laser welding method of claim 1 further comprising causingthe laser to shut off in response to sensing a condition proximate theat least one movable mirror.
 15. The laser welding method of claim 14wherein the sensed condition is a thermal condition.
 16. The laserwelding method of claim 1 further comprising delivering gas to a weldsite from a gas assist accessory mounted on the laser welding head. 17.A laser welding method comprising: generating a raw laser beam from alaser; collimating the raw laser beam in a laser welding head; movingthe collimated beam relative to a workpiece with a wobble pattern in alimited field of view; focusing the moving beam on the workpiece as thebeam moves with the wobble pattern; and moving at least one of the laserwelding head and the workpiece relative to each other while moving thebeam on the workpiece in the wobble pattern to perform welding.
 18. Thelaser welding method of claim 17 wherein the movement is only within alimited field of view defined by a scan angle of about 1-2°.
 19. Thelaser welding method of claim 17 wherein the wobble pattern is selectedfrom a group consisting of a circular pattern, a FIG. 8 pattern, a zigzag pattern, and an undulating pattern.
 20. A laser welding methodcomprising: providing a laser for generating a raw laser beam; providinga laser welding head for collimating the raw laser beam in a laserwelding head, moving the collimated beam relative to a workpiece with awobble pattern in a limited field of view, and focusing the moving beamon the workpiece as the beam moves with the wobble pattern; andproviding at least one motion stage for moving at least one of the laserwelding head and the workpiece relative to each other while moving thebeam on the workpiece in the wobble pattern.